Felix, the 8-year-old boy, learned to surf when he was two years old.
In this sentence, the phrase "the 8-year-old boy" is a nonrestrictive element, providing additional information about Felix but not essential to the meaning of the sentence. The commas before and after "the 8-year-old boy" indicate that it is a nonrestrictive element, and the sentence would still be grammatically and semantically complete without it.